Another day, another secret celebrity engagement!
The couple "decided to take their relationship to the next level," a source told the magazine. Theron, 39, and Penn, 54, first stepped out together a year ago in December 2013.
It's been quite easy for the couple to keep their engagement under wraps since there is reportedly no engagement ring.
This would be the third marriage for Penn, who was married to Madonna for four years and to Robin Wright for 14 years.
Theron has never been married before and has spoken out about her feelings against a typical marriage. "Let's put it this way: I never had the dream of the white dress. And watching other people getting married? I think it's beautiful for them, but to be quite honest, usually I'm sitting there just devastated," she told Vogue in June. "It's supposed to be this night of celebrating love, and all you see is a couple separated all night making sure everybody else is okay. It just looks like a lot of work. And as you get older, you start sifting through the stuff that really matters."
Best of the Year! See TV's most memorable kisses: